Deployment of Entanglement-Based QKD in Financial Infrastructure

This study reports on the practical integration of entanglement-based quantum key distribution (eQKD) into existing, high-security financial infrastructure. While QKD is often demonstrated in laboratory settings, deploying it in real-world metropolitan fiber networks presents significant challenges, including environmental noise, fiber-induced polarization drift, and the need for long-term, autonomous operation. The authors addressed these by designing a robust, passively stable source of polarization-entangled photon pairs and an automated post-processing pipeline that interfaces directly with a key management system (KMS).

The system connects two data centers via a 22 km fiber link with 8 dB of loss. It utilizes a polarization-entangled source based on spontaneous parametric down-conversion (SPDC) and superconducting nanowire single-photon detectors (SNSPD). To maintain performance without external reference lasers, the system employs active polarization control that triggers whenever the quantum bit error rate (QBER) exceeds 2%. Timing synchronization is achieved by exploiting the intrinsic temporal correlations of the entangled photon pairs, eliminating the need for external high-precision time references. The classical post-processing chain—including parameter estimation, error correction via low-density parity-check (LDPC) codes, and privacy amplification—was fully automated to ensure continuous key delivery to the financial institution's VPN infrastructure.

Over a four-month deployment period, the system achieved an uptime of 93.7%, with no downtime attributed to the quantum optical components. The system maintained a consistent average secure key rate of 63.8 kb/s. The active polarization control successfully kept the QBER below 2% for 97.4% of the operational time, demonstrating that eQKD can be integrated into existing, non-laboratory environments with minimal manual intervention. The generated keys were successfully utilized to establish secure VPN tunnels, proving the viability of eQKD for protecting critical financial data.